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Compasses don't work on Mars, so how do you navigate?

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Re: Compasses don't work on Mars, so how do you navigate?

#71

Post by planteen »

kefka wrote: post #58
gliese1337 wrote: post #34

I am surprised that no one has yet mentioned the Gyrocompass: https://en.wikipedia.org/wiki/Gyrocompass The post mentions manually-set directional gyroscopes, but gyrocompasses are a step ahead of that; on any sufficiently-quickly-rotating planet, a gyrocompass will point you towards the geographic poles by noting the axis of precession of a gyroscope with arbitrary orientation. That's even better than a magnetic com…

Maybe you would know, but are MEMS gyroscopes of accurate quality to output true north data? Specifically referring to Invensense 9150 9dof (3 accel, 3 magnetometer, 3 gyro)

Not for very long at decent accuracy. My of the hip guess is minutes. The zero rate output is +/-20 deg/s for the part you listed with RMS noise of 0.02 deg/s.

Re: Compasses don't work on Mars, so how do you navigate?

#72

Post by Sanddancer »

scott_karana wrote: post #10
msandford wrote: post #6

Earlier quoted context omitted.

Further if you're not looking for realtime direction finding and you're willing to wait a few minutes for a fix, you can get away with far fewer satellites. Putting 6 small satellites in orbit and getting position fixes every hour would still be way better than nothing.

How would the satellites themselves maintain their proper positions relative to Mars, without ground stations to orient against?

Neutron stars -- http://www.nasa.gov/topics/universe/features/zombie-stars-si...

Re: Compasses don't work on Mars, so how do you navigate?

#73

Post by kefka »

planteen wrote: post #71
kefka wrote: post #58

Earlier quoted context omitted.

Maybe you would know, but are MEMS gyroscopes of accurate quality to output true north data? Specifically referring to Invensense 9150 9dof (3 accel, 3 magnetometer, 3 gyro)

Not for very long at decent accuracy. My of the hip guess is minutes. The zero rate output is +/-20 deg/s for the part you listed with RMS noise of 0.02 deg/s.

Hmm.

A group of us at our local hackerspace is building an autonomous robot. We already have that 9DoF sensor as well as a GPS and barometer.

I'm able to accurately calculate where North(magnetic) is, as well as down, and roughly what altitude I am, and synchronize them to sporadic GPS locks. Depending how useful, this could be good at providing North(true). I'll see if any sort of calibration would be useful (considering I know my lat/lon and can calculate the expected rotational vector).

I'm investigating using ORB-SLAM with ROS to also provide accurate locations of the localization.

The whole idea is that I can use this as yet another piece in a probability-location detection as well as map other things quickly and accurately.

Re: Compasses don't work on Mars, so how do you navigate?

#74

Post by batou »

kefka wrote: post #60
batou wrote: post #53

Earlier quoted context omitted.

Interesting thought. Never considered that you have planet specific propagation.

Well, depending on frequency you would still have some traversable effects regarding radio. You would have ground wave propagation at the minimum. unfortunately, most radio would be line of sight because of no atmosphere. Limited atmospherics would provide very restricted use on a multitude of frequencies mainly lower than 6 meter. If you wanted to communicate with the other side of the body, you would have to rely o…

Very interesting. Thanks for the detailed reply.

Re: Compasses don't work on Mars, so how do you navigate?

#75

Post by darkmighty »

hamiltonkibbe wrote: post #63
darkmighty wrote: post #59

Earlier quoted context omitted.

The gyrocompass orientation should, in principle, be obtainable by properly integrating gyroscope readings (and accelerometer? not sure if required).

You still need a way of determining the initial position/pose

I don't think so. The gyrocompass relies on gyroscopic precession. The precession itself can be obtained by integration, which gives orientation. Of course, the precision of this process may well be very low or unusable.

Re: Compasses don't work on Mars, so how do you navigate?

#76

Post by mikeash »

lmm wrote: post #66
mikeash wrote: post #41

Earlier quoted context omitted.

Interesting tidbit about Mercury's rotation: although it's clearly visible to the naked eye and thus has been known since before the dawn of recorded history, and has been observed through telescopes since telescopes were invented, the fact that it is not tidally locked has only been known since 1965.

Mercury is pretty featureless, right? It's not like Jupiter where you could see the rotation just by keeping track of the Great Red Spot.

It has lots of craters and such. I don't know what it looks like through an older telescope. According to Wikipedia, the problem was that because the rotation is in a resonance with its orbit, and because it's so close to the sun and thus can only be observed at certain times, it was always observed when in just one orientation.

Re: Compasses don't work on Mars, so how do you navigate?

#77

Post by scott_karana »

afarrell wrote: post #19
scott_karana wrote: post #15

Earlier quoted context omitted.

Yeah, agreed, my comment was meant to politely point out the necessity to the people thinking we could get away with "dropping a few satellites" ;)

All of these things can be done remotely without any wetware on Mars.

"How?"

Re: Compasses don't work on Mars, so how do you navigate?

#78

Post by planteen »

kefka wrote: post #73
planteen wrote: post #71

Earlier quoted context omitted.

Not for very long at decent accuracy. My of the hip guess is minutes. The zero rate output is +/-20 deg/s for the part you listed with RMS noise of 0.02 deg/s.

Hmm. A group of us at our local hackerspace is building an autonomous robot. We already have that 9DoF sensor as well as a GPS and barometer. I'm able to accurately calculate where North(magnetic) is, as well as down, and roughly what altitude I am, and synchronize them to sporadic GPS locks. Depending how useful, this could be good at providing North(true). I'll see if any sort of calibration would be useful (consid…

Yeah using a compass and a magnetic field model using GPS position should let you estimate the bias from the gyro.

Re: Compasses don't work on Mars, so how do you navigate?

#79

Post by yellowapple »

jameshart wrote: post #70
yellowapple wrote: post #35

Earlier quoted context omitted.

Doesn't Mars have clouds, though?

Dust clouds, maybe. Water clouds, no, not at all.

That's actually not correct: http://mars.jpl.nasa.gov/MPF/science/clouds.html

They're pretty much all cirrus-equivalents, granted, but they're still water (more precisely, water ice) clouds. That is, unless NASA is misinterpreting them, but seeing as they're, like, the end-all-be-all experts on Martian climate, I reckon that's unlikely.

Even barring that, however, dust clouds would also cause issues for celestial navigation.

Re: Compasses don't work on Mars, so how do you navigate?

#80

Post by hamiltonkibbe »

darkmighty wrote: post #75
hamiltonkibbe wrote: post #63

Earlier quoted context omitted.

You still need a way of determining the initial position/pose

I don't think so. The gyrocompass relies on gyroscopic precession. The precession itself can be obtained by integration, which gives orientation. Of course, the precision of this process may well be very low or unusable.

you don't need an initial heading measurement but you still need to know where you are
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